1. Field of the Invention
The present invention relates to a fuel property detecting apparatus for detecting a property of fuel supplied to an internal combustion engine.
2. Description of Related Art
A usual gasoline engine mounted on vehicle are mostly arranged that an intake pipe is equipped with a fuel injection valve. Fuel (gasoline) is injected into an intake port. In this intake port injection system, a part of fuel injected from the fuel injection valve is directly introduced into cylinders. The rest of fuel adheres on an inner surface of the intake port and a surface of an intake valve, and it gradually evaporates and is introduced into the cylinders. Accordingly, the amount of fuel introduced into the cylinders varies according to an amount of evaporating fuel which adheres on the inner surface of the intake port or the like (wet). The amount of evaporating fuel (rate of an evaporation) varies according to the property of fuel, but the property of fuel is not stabilized even among the same kind of fuel. The property is different between makers, and is changed according to the season and sales area even in the same makers fuels. Accordingly, it is necessary to detect the fuel property in order to provide an accurate air-fuel ratio control (fuel injection control) by considering the amount of evaporating fuel.
It is proposed that the fuel property is detected on the basis of each of parameters such as an ability to start, a variation of the rotation and a rising of the rotation as described in JP-A-9-203342.
However, the ability to start, the variation of the rotation and the rising of the rotation are varied according to various factors except for the fuel property. Therefore, it is impossible to detect the fuel property accurately, even if the fuel property is detected by using these parameters, since it is influenced by the various factors except for the fuel property. For instance, in a manual-mission car, there are possibilities of an erroneous detection, because the variation of the rotation and the rising of the rotation varies a lot according to a shift-operation by driver.
As a result, a driveability, a fuel consumption and an emission might become worse, since an accuracy of a correction by the fuel property is lowered.